As someone who maintains his own custom theme and uses some less-advertised features of Hugo for his blog, I fairly frequently find out a day or two later that my blog hasn’t been building for a bit and a bunch of posts are stacked up. This is always my fault, but because the build failure is on the Design page, I often simply don’t know that I messed up.
I would love the option to get an email notification or even app-based push notification if a build of my blog fails so I know to investigate.